An inkjet recording system is a recording system that directly discharges an ink droplet onto a recording member from a significantly minute nozzle, and causes the ink droplet to adhere to obtain a character or an image. According to the system, there is a merit in that a device in use is quiet, and operability is excellent, and a merit in that it is easy to colorize, and plain paper may be used as the recording member. Thus, the system is widely used as output equipment in an office and home. On the other hand, a digital printing is expected to be used as output equipment due to an enhancement of an ink-jet technology in industrial use, and an aqueous pigment ink is desired in terms of environment, tolerance of a printed material, and the like.
Referring to the aqueous pigment ink, since a pigment is insoluble in water, dispersion stabilization in water is attempted using a dispersing resin to maintain dispersion of the pigment in an ink (for example, see Patent Literatures 1, 2, and 3). In addition, in a case of the inkjet recording system, a water-soluble solvent which is regarded as a moisturizing agent and has a high boiling point is contained to prevent drying of a nozzle.
In general, in a drying mechanism of a water-color ink, an ink impacts on a base material, and then is divided into permeation into the base material and evaporation. However, contribution to permeation is extremely great, and permeation of an ink is slow in a base material having a high hydrophobicity such as coated paper, art paper, and a vinyl chloride sheet. Thus, in a case of multicolored printing, color mixture of inks occurs, and there are problems in that a clean image may not be formed, a printing speed may not be increased, and the like. For this reason, there is a need to attempt to enhance a drying characteristic by adding a water-soluble solvent having a high boiling point and a high permeability to an ink.
However, adding a permeable solvent to an ink may change a dissolved state of a dispersing resin that stabilizes a pigment dispersion state, and significantly degrade pigment dispersibility and preservation stability.
That is, there has been a desire for a combination of a solvent having a high permeability and a pigment dispersing resin that does not degrade pigment dispersibility even when the solvent is present.
In addition, C.I. Pigment Yellow 150 is used and in practical use as a yellow pigment having a high weather resistance in an inkjet solvent ink and the like, and is rare in a water-color ink due to a low dispersion stability.
Patent Literature 4 discloses a water-color ink in which C.I. Pigment Yellow 150 is dispersed using a surfactant. However, dispersion stability is predicted to decrease in a dispersion using a surfactant when mixed with a solvent having a high permeability. For this reason, a permeable solvent may not be added, and practical use may not be achieved in printing on a base material having a high hydrophobicity such as coated paper and vinyl chloride sheet. Patent Literature 5 discloses a water-color ink stabilized by dispersing C.I. Pigment Yellow 150 using a pigment dispersing resin. Dispersion stability is deemed to be maintained even when mixed with a solvent having a high permeability since a pigment dispersing resin is used. However, a great amount of solvent occupies an ink, drying is significantly slow on a base material, and color mixture occurs between inks. Thus, a good-quality printed material may not be obtained on a base material having a high hydrophobicity.
In addition, a pigment having an excellent weather resistance is limited among magenta pigments. However C.I. Pigment Red 122 is excellent among magenta pigments. However, referring to C.I. Pigment Red 122, a great number of pigments have a hydrophilic surface when compared to another color. Thus, it is difficult to manufacture an ink having an excellent dispersion stability so far. In particular, it is much more difficult to ensure dispersion stability when a solvent having a high permeability is used.
That is, there is a desire for an ink capable of maintaining dispersion stability even when a solvent having a high permeability is present in C.I. Pigment Red 122 having an excellent weather resistance.